In the drilling of oil and gas wells it is advantageous to be able to pass large diameter drill bits and bits which are slightly oversized through the landing shoulder bore of a wellhead member. While it might be suggested that boring out the wellhead member to pass such bits would be a solution to this problem it would reduce the strength of the member and its pressure rating. Reduction of the size of the landing shoulder alone would reduce the load carrying capacity of the landing shoulder.
One attempt to increase the through bore for the passage of large diameter bits and slightly oversized bits or various downhole pieces of equipment is disclosed in U.S. Pat. No. 3,684,016. Such patent suggests a split support ring that deflects radially outward into a groove in the wellhead hanger body. However, such construction, while possibly supplying adequate support has tendencies for the split ring to catch prematurely, or not all if the recess is filled with unexpected deposits.
Another example of a string hanging system is shown in U.S. Pat. No. 4,295,665. Such system includes a locking ring 60 which is a split ring spring biased to move outward and coacts with a shear pinned lock positioning element 97 which is a split spring biased inwardly. The element 97 includes grooves on its surface 110 to restrict the development of radial forces against the interior of the casing suspension collar 22 and also outer upwardly facing teeth 114 which are recited to engage the casing to transfer a portion of the weight into the outer collar 22. Such description set forth in such patent is believed to be contradictory in that one portion (grooves on surface 110) is to restrict the development of radial forces and the other (teeth 114) is to transfer radial forces to collar 22. Further upwardly directed teeth 114 will have a minimum of load bearing capacity as compared to downwardly directed teeth usually provided in hanger slips. Difficulties can develop if the locking ring recess is blocked by deposits or if it can possibly catch on joints or other grooves in the collar.